wifi: ath12k: Add support to set per-radio RTS threshold

wifi: ath12k: Add support to set per-radio RTS threshold

Currently, command to set RTS threshold makes changes to the threshold of
all radios in the multi-radio wiphy. But each radio in a multi-radio wiphy
can have different RTS threshold requirements.

To support this requirement, use the index of radio for which the RTS
threshold needs to be changed from mac80211 - radio_idx. Based on the value
passed, set the RTS threshold value for the corresponding radios. Following
are the possible values of radio_idx and the corresponding behavior in
multi-radio wiphys:
 1. radio_idx is -1: consider RTS threshold as a global parameter, i.e.,
    make changes to all the radios in a wiphy. If setting RTS threshold
    fails for any radio, then the previous RTS threshold values of
    respective radios will be restored.
 2. radio_idx denotes a specific radio: make changes in RTS threshold to
    that radio alone.
 3. radio_idx is any other number: report it as an invalid number.

In case of single-radio wiphys, continue with the existing behavior, i.e.,
set the passed RTS threshold value to the radio present.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Roopni Devanathan <quic_rdevanat@quicinc.com>
Reviewed-by: Baochen Qiang <baochen.qiang@oss.qualcomm.com>
Link: https://patch.msgid.link/20250826105714.1188131-1-quic_rdevanat@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>